1. Field of the Invention
The present invention relates to an image pickup apparatus and an image pickup system using the same and, more particularly, to an image pickup apparatus in which a plurality of photoelectric conversion portions are arranged in a common circuit and an image pickup system using this apparatus.
2. Related Background Art
Digital broadcasting has started in the U.S.A in 1998. In 2006, NTSC broadcasting (525V) will be obsolete and TV broadcasting will completely shift to HD digital. In addition, digital cameras with 1,300,000 pixels are sweeping over the market. This means that there is a demand for outputting high- and low-resolution signals from a high pixel count sensor as needed.
Under these circumstances, the pixel size in CCDs is shrinking (reducing). However, a CCD with a side of about 5 μm is incapable of high-speed read. CCDs currently commercially available have only 600,000 pixels and a read rate of about 60 frame/sec.
CMOS sensors manufactured by the same process as the CMOS manufacturing process allow random access and have been expected as sensors suitable for higher-speed operation in the future.
When a small number of pixels are to be read out from a high pixel count sensor, low pixel count information can be obtained by interlaced scanning. In this interlaced scanning,    (1) A CCD discards pixel signals of unnecessary horizontal lines to an overflow drain provided in a horizontal shift register. Additionally, of signals read out from the CCD, only necessary signals are sampled.    (2) A CMOS sensor outputs only necessary signals by random access.
However, interlaced scanning (1) of the CCD requires excess power to transfer charges of unnecessary pixels. In addition, since unnecessary signals are discarded by decimation, moiré due to low sampling rate occurs. Interlaced scanning (2) also generates moiré.